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Researchers have found that two of the most important coral species forming Florida's reef are now functionally extinct after a withering ocean heatwave led to devastating losses.

The Meaning Behind 'Functional Extinction' Signifies

The almost complete collapse of these corals, which once served as the foundation of reefs in Florida and the Caribbean, indicates they are no longer able to play their previously crucial role in building and sustaining reef ecosystems that host a diversity of marine life.

Functional extinction is a stage preceding total extinction, a threat that now hangs for many coral species.

Scientists recently warned that a critical threshold has been crossed, whereby corals around the world are likely to be wiped out due to climate change, which is raising ocean temperatures to intolerable levels.

Researcher Perspective

"Time is running out," said Ross Cunning of the recent research. "Extreme heatwaves are becoming more frequent and intense due to global warming, and absent immediate, ambitious actions to slow ocean warming and enhance coral survival, we risk the disappearance of additional coral species from reefs in Florida and worldwide."

Details of the New Research

The recent study, featured in the Science journal, examined the fate of staghorn coral and elkhorn corals off the Florida coast following a severe marine heatwave in 2023.

This event elevated temperatures on Florida's deteriorating coral reefs to their peak temperatures in more than a century and a half.

The two species are complex, reef-forming corals and are identified because they resemble, respectively, the horns of male deer and elk.

However, researchers who conducted diver surveys of over fifty-two thousand colonies of the species, across nearly four hundred sites along Florida's coast, found extensive, often catastrophic, losses.

Geographic Impact

• Along the Florida Keys, mortality rates reached 98% and even 100%, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been lower, death rates were lower, at about thirty-eight percent.

Historical and Current Dangers

The two Acropora species had already suffered from decades of regional pressures in Florida, such as poor water quality from pollutants that wash off the land, as well as illness.

But the 2023 heatwave has been fatal for these heat-sensitive species.

The 2023 event caused the ninth occurrence of bleaching on the Florida reef – a process whereby corals become heat-stressed and expel the symbiotic algae living in their tissues, causing them to become bleached white.

If temperatures remain elevated, the corals perish entirely.

Worldwide Implications

Globally, coral reefs are among the ecosystems most vulnerable to the anthropogenic climate emergency.

This poses a significant danger to:

• A quarter of all ocean life that depends on what are effectively the rainforests of the sea.
• Hundreds of millions of people who depend upon corals to support fish that they can eat and gain an income from.

Corals also act as a barrier to protect our shorelines from intense hurricanes, which are themselves being intensified by rising global temperatures.

Conservation Attempts

In a last-ditch effort to prevent a death spiral of endangered corals, scientists have created repositories of Acropora in aquariums and ocean-based nurseries.

Efforts have been undertaken to reseed corals on reefs in Florida, as well, in an effort to restore some of the ninety percent of coral cover disappeared off the state in the last forty years.

But as global heating continues to intensify, there is slim chance of continued existence of these species without major interventions, researchers warn.

Further Expert Commentary

"Elkhorn species, especially, are some of the most important wave-breaking coral species in the area," noted Andrew Baker, a marine biologist at the University of Miami.

"They used to be abundant on shallow reef tops in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from flooding during storms, it is worthwhile taking exceptional steps to ensure we don't lose these corals completely."